Adjective
(medicine) In a decubitus position: lying down; thus:
(medicine, broadly) Any position of lying down.
Synonym: recumbent
(medicine, less broadly) A position of lying on one's side, in contrast with supine or prone positions of lying down.
Coordinate terms: supine, prone
(medicine, dated) Relating to a pressure ulcer (a decubitus ulcer, that is, a bedsore).
Source: en.wiktionary.org